1. Field
Embodiments of the present invention generally relate to systems and methods for producing ammonia and urea. More particularly, embodiments of the present invention relate to systems and methods for the integrated production of ammonia and urea.
2. Description of the Related Art
Urea is synthesized by reacting ammonia and carbon dioxide at high pressure to form ammonium carbamate, which is subsequently dehydrated by applying heat to form urea and water. The reaction of ammonia and carbon dioxide to form urea involve the following equilibrium reactions:2NH3+CO2NH4CO2NH2 (ammonium carbamate, exothermic)NH4CO2NH2H2O+NH2CONH2 (urea, endothermic)
The first reaction producing ammonium carbamate is an exothermic reaction and essentially goes to completion. The second reaction for producing urea is endothermic and does not go to completion. The conversion of ammonium carbamate to urea increases as the temperature and NH3/CO2 ratio increase and decreases as the H2O/CO2 ratio increases. The resulting product can be a urea solution containing urea, water, and unconsumed reactants, which include ammonium carbamate, ammonia, carbon dioxide, and water.
A large part of the ammonia produced throughout the world is utilized for the production of urea. This large use of ammonia has prompted the integration of both the ammonia plant and the urea plant. However, the present ammonia and urea integration schemes, while seemingly attractive, have serious disadvantages. For example, a number pieces of equipment used in the urea production section must be operated at high pressures and temperatures, shutdown of the urea section can necessitate shutdown of the ammonia section, a large amount of energy in the form of heat (e.g. steam) and pressure (e.g. compressors) are required to operate the urea section, and other economically negative impacts are present.
In view of the above, a need, therefore, exists for improved methods for integrated ammonia-urea production.